Similarly, when the Wall Street Journal hailed Tony Blair as "America's chief foreign ambassador" it did little to enhance the reputation of a man determined to "heal the world". So when Norman Tebbit praises the home secretary on his "vision" of race in Britain, David Blunkett should take it as a sign that something is seriously awry.

"We should all be grateful to Mr Blunkett for stating what most of us had long believed," Tebbit says. "Had I proposed English tests and a loyalty pledge, the race-relations warriors would have called for me to be expelled from the Tory party and excluded from decent company." Quite.

On the third anniversary of the Macpherson's report into the death of black teenager Stephen Lawrence, the government's understanding of race and racism is regressing towards the pitiful level it was before Stephen's birth in the 1970s.

Like the Yarl's Wood detention centre, current race policy is a response to the most base and discriminatory instincts of populists rather than the potential for equality of opportunity and humanism enacted by progressives. And like Yarl's Wood it is destined to fall in a smouldering heap - a pyre created by the desperate as an epitaph for those who have little or nothing to lose.

Three years ago Britain started to engage in a national conversation about how it could tackle the racism afflicting its institutions and infecting its private, public and popular culture. Today the pendulum of racial discourse is swinging back to an altogether more complacent and less challenging era.

We are returning to the crude and flawed mythology of a mono-racial, culturally uniform British identity in which non-white people's presence is tolerated - and even then only conditionally.

The journey has not been straightforward and its destination is by no means inevitable. The past year in particular has seen changes, both stark and subtle, of emphasis in the race debate. In tone, tenor and content, the focus has shifted from race to religion, colour to creed and ethnicity to economics.

Moreover there remain major differences both in perception and reality between the young and the old, the north and the south, urban and rural areas and, increasingly between different ethnic groups.

A young British-born Bangladeshi in Burnley will have little shared experience with an Indian pensioner in Slough, let alone an Afro-Caribbean in Bristol; similarly, white teenagers in Shropshire will have a very different understanding of how Britain's racial landscape is changing compared to their counterparts in Birmingham.

But for all the complications and nuances a general trend is none the less clear. Three years ago racism was regarded as the problem. Now, once again, the very existence of Britain's ethnic minorities is becoming the problem. The right of Muslims to live in this country has been openly questioned and is regularly qualified.

The answer to racially-charged disturbances in our northern cities is not urban regeneration but language classes and citizenship lessons for new immigrants - never mind that, like their white adversaries, the vast majority of the Asian youth who took to the streets were born here.

With his advice that Asians should marry people from inside the country rather than the Indian subcontinent, the home secretary even wants to legislate for love. But if the standard of race debate has fallen far it has also fallen fast.

Ever since the release of the report there has been a rump of malcontents who expressed impotent rage at Macpherson's recommendations. Fearful of the implications of his findings, they damned the future without being able to defend the past or justify the present. But this disgruntled minority has grown in both size and confidence.

Last March the judge in the trial of three Leeds footballers was sufficiently emboldened to denounce Macpherson's definition of a racist attack ("any incident which is perceived to be racist by the victim or any other person"). He said: "The risk of police using [the Macpherson definition] in their investigations in the absence of evidence has the potential for causing serious mischief and ought to be reconsidered."

Two unrelated but mutually reinforcing events have accelerated this trend. The first is racial disturbances in May and June in our northern cities - the product of longstanding economic decline and social alienation of Pakistani, Bangladeshi and white communities. The second is the sudden and symbiotic rise in both Islamic fundamentalism and Islamophobia, prompted first by the terror attacks on September 11 and then by the war in Afghanistan.

To this tinderbox add an inflammatory new home secretary. Blunkett appears to have either misunderstood, or just plain missed, the debates on race, nationality and ethnicity that have been taking place for the past 20 years.

Using "political correctness" and bemoaning "white, middle-class" guilt makes him sound more like a caller to radio phone-in programme than a government minister. "We have norms of acceptability," he said shortly before December's reports into last year's disturbances. "And those who come into our home - for that is what it is - should accept those norms just as we would have to do if we went elsewhere."

He talks as though he has yet to learn that more than half of the non-white people who live in this country were born here. Second and third generations who have been trying to turn Britain from a house into a home are once again being shown the visitors' entrance. He comes across as the sort of man who used to approach you at the bus stop in winter, full of the joys of Jim Davidson and say: "Cold isn't it? Bet it's not like this where you come from."

His suggestions for language courses and US-style citizenship classes have merit in a debate about social inclusion - there are many white people who need language and literacy courses too, but not as a response to addressing Britain's race relations.

Stephen Lawrence could speak better English than the thugs who killed him. And if anyone needed citizenship lessons it was the assailants' parents who raised such hateful, racist criminals as children - not the determined, eloquent, Neville and Doreen Lawrence.

But at the heart of the problem lies not his lack of understanding of the experiences of blacks and Asians but his woefully simplistic notion of what it means to be British. He speaks of citizenship as though there is any consensus as to what "citizenship" actually means in a nation of subjects to the crown, without a written constitution and struggling with devolution, European integration, globalisation and the decline of the monarchy.

He refers to arranged marriages to foreigners as though they are something alien to British culture: of the six British monarchs of the last century five married foreigners and most of those unions were arranged. He wants new immigrants to sign up to an identity that those who have lived here for centuries cannot agree on.

In the tradition of Tebbit he might claim that he is thinking the unthinkable. But in light of the embers at Yarl's Wood, he is working towards the unworkable and, for a Labour government, the unforgivable.